Mill scale removal ?

[Dabbler]

sorry about the misspelling I normally know better.

I understand that oxalic acid works a little faster, and is cheaper, but I haven't tried it yet. My only experience is with citric.

 

[Janger]

@Dabbler let's see some before / after pictures of mill scale and rust removal with citric acid? run an experiment for us?

 

[Dabbler]

run an experiment for us?

when I get the chance. On another thread I show how busy I am trying to vent my attic.

 

[phaxtris]

Sandblast that sucker

 

[George]

You could try a fine flap disk in the grinder, to remove rust i have a 65 ltr tote with water and a cpl of tablespoons of bicarbonate soda powder and i use an old Blackberry phone charger cathode and anode = apiece of rebar at one end and a piece of old sheet metal at the other tie or connect anything i want derusting to it and plug it in and leave for a day 6v 600 milliamperes works great lots of YouTube videos showing how to do it

 

[Janger]

Ok more info on this process. I got some citric acid from my spouse - a bag of crystals. See the pic for where to get it and how much. I put 1/4 cup into 2 cups of warm water and threw in some 1/2" square bar. I also tested 7.5% vinegar with the same material. Results are very similar over about a 24 hour period. You can see all the mill scale floating in the bag. I then took some sand paper to it and cleaned it up some more. I decided to put it back in the citric acid to see what happens with another day in solution. The picture shows the treated bar on the left and an untreated bar on the right. The picture does not really do it justice - I think 70% of the mill scale came off with a little rubbing. By the way - wear gloves - it's filthy like decaying rubber plumbing parts and stains your hands.

Best thing about citric acid - it does not smell so strong - and I think awful - like vinegar does. I'll be using this in the future I think.

 

[CalgaryPT]

Thanks John. I wonder if the degree of difficulty varies with the alloy? I only ask because I had a big piece of 1/2" plate once that was some odd grade for me and it was impossible to even sand the mill scale off.

I'll bet the citric acid solution works well to remove zinc plate as well. In a pinch I once used Real Lemon juice on some galvanized bolts. Worked OK—and smelled nice too.

 

[Janger]

Ok I have been trying citric acid again. I left a bunch of bar stock in it for maybe a month. The sides and bottom cleaned up amazingly well. But the top stayed pretty dark. So I thought hey how about doing again with even more citric acid. I made a stronger solution and poured it on top. It very quickly over night precipitated out all the minerals and the metal looked like the humidifier pan. And also the mill scale seemed to be back on the metal too! Disaster! now it’s worse than ever. Ok back to vinegar. After an overnight session the vinegar seems to have dissolved the minerals and loosened the scale. I’ll wash it up and see what happens.

The bar I’m holding is very clean. That was after a month of Citric acid soak.

 

[PeterT]

I used these 60 grit purple pads to remove mill scaled on HRS plate prior to painting just with my little Milwaukee cordless grinder & it was done in no time. Smooth metal, nice texture. I guess if you have nooks & crannies like a grate It may not lend itself to grinders through. How about that drive-up sand blast place people talk about?

https://www.amazon.ca/gp/product/B07K19L38B/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

https://www.amazon.ca/DUROPEAK-10Pa...6614b&pd_rd_wg=P7f4I&pd_rd_i=B07X2Z9MQB&psc=1

 

[Crankit]

I heard of these off of Welding Tips and Tricks YouTube channel so I tried one...I'm impressed!

https://www.walter.com/en_CA/products/abrasives/blending/flexcut-mill-scale

 

[George]

Me, i use an old blackberry charger, lump of old steel at one end with a piece of steel wire, and the item i need derusting at the other end also wire attached, or if it’s a few items i place them in an old deep fat fryer basket and attach the Negative of the chargers cut cable, then the positive wire to the cathode, charger is 5V 600 milliamperes, cpl of tablespoons of baking soda fill the tote with water, plug it in and go back a cpl of days later, Hey presto rust is attracted to the cathode and your part/ parts are just in need of a wipe down.

 

[Dabbler]

I understand that electrolysis works best for black or orange rust. Mill scale is composed of a bunch of impurities and carbides that seem to not respond well to that process...

Is your experience different?

 

[George]

Not at

I understand that electrolysis works best for black or orange rust. Mill scale is composed of a bunch of impurities and carbides that seem to not respond well to that process...

Is your experience different?

The electrolysis process breaks down the rust and any other impurities on or around it also break free and just float on the top of the water, i have attached an image of 2 old MT3 dead centres and a unknown sized reamer, note the non magnetic crap floating in the plastic tub, this is after just 12 hours, i shall wash them and post the results later today.

Last picture taken 10 am after 12 hours in the tub, light scrub with wire wool, perfectly useable

 

[Janger]

Hi George
Care to run your experiment again with a piece of hot roll steel that has a good cake of mill scale?
Thanks!
John

 

[Janger]

Back to the endless mill scale removal saga. I saw a youtuber swearing this 3M product is excellent, fast, and lasts a long time. Anybody using them for mill scale removal?

3M 5" Scotch-Brite Clean and Strip XT Pro Disc - Depressed Centre - XC

Scotch-Brite Clean and Strip XT Pro discs are highly conformable—this provides larger contact area and faster removal. These discs provides uniform, consistent finishes while being gentle on parts.Large contact area for fast removal ratesConforms to

www.kmstools.com

 

[Dan Dubeau]

I haven't used the 3m version, but having tried princess auto version I'm sold. I can only guess that the 3m version lasts a bit longer, based solely on speculation and past experiences with other kinds of import abrasives.

I'm not normally a fan of import abrasives and consider them a false economy, but having bought one on a whim, I just ordered a bunch more.

 

[Dabbler]

I'm a big fan of a Critrus bath presoak, and one of these days I'm interested in getting some EDTA to make the solution closer to neutral pH and making it more effective.

 

[Ironman]

I am surprised that you cannot get a ground through the mill scale. I always can. Now, that #**@! powder coat stuff...

 

[YotaBota]

I was playing with the vinegar and man it works well,,,, if you have time. Here are couple of pieces cut side by side from the same plate after a two day soak. I know I didn't need to leave the soak that long but got busy with other things.

After the soak was a quick cleanup with the wire brush on the 4 1/2 inch angle grinder.
The pieces are leftovers from the bumper build, the guy at the blasting shop said it was some of the toughest mill scale he's ever seen but the vinegar didn't have any problems with it.
I hit the done piece with the primer right away as it was mentioned earlier that the rust will set in quickly.

 

[Ironman]

I understand that electrolysis works best for black or orange rust. Mill scale is composed of a bunch of impurities and carbides that seem to not respond well to that process...

Is your experience different?

I de-rusted a complete JD Model B with my battery charger. It removes paint very well also.